We will study the factors(s) involved in the control of vascular endothelial cell proliferation and differentiation, as well as the events, triggered by those factors, which lead to the proliferation and subsequent differentiation of these cells. We will study the effect of FGF on the synthesis of specific cytoplasmic proteins during the G 1 phase on the cells and correlate the mitogenic effect of FGF with possible phosphorylation events taking place within the cell membrane. We will study the relative importance of FGF binding to specific cell surface receptor sites by insertion of FGF directly into sparse cultures of vascular endothelial cells using FGF encapsulated in liposomes. We will also insert the FGF encapsulated in liposomes directly into confluent monolayers of vascular endothelial cells. We will study the correlation between cessation of growth and the reorganization of the cells into a monolayer and the appearance in the cell surface membrane of CSP-60, and we will explore further the events which lead to the appearance of this cell surface protein when endothelial cells become confluent. The effect of FGF on the non-thrombogenic surface, PGI2, and production and polarity of cell surfaces of confluent monolayers of vascular endothelial cells will be analyzed and compared to the effect of platelet release material and platelet-made extract. The effect of the close association of the endothelium with smooth muscle cells will also be analyzed in a tri-dimensional model.